The great benefit of a watch is that you can check the time quickly without being obvious about it. This is important when you are meeting with clients or involved in any other kind of important or potentially sensitive transaction: pulling out your phone to check the time is rude and disruptive, but you often need to know how much time has elapsed so you can bring the meeting to a close if you need to.

I'm often on a tight schedule and being able to check the time once or twice during a meeting without the client noticing is valuable.

Also, they look nice. And if they make me look older, and therefore more experienced, so much the better!